The importance of the control of plant pathogens, nematodes and weeds cannot be underestimated in the agriculture industry. Therefore, a complete destruction of plant pathogens or at least a substantial reduction is an often-encountered challenge in the agriculture industry. Pathogenic organisms afflict root systems of various kinds of crops and severely inhibit their growth, causing severe damage to the plants. In order to circumvent these problems, different mechanisms are often adopted to control the harmful effects of pathogenic organisms on plants and to enhance the productivity and improve the viability of plants.
Traditional methods such as crop rotation or fallowing the fields for as long as four years and use of pathogen-resistant crops are among the most common methods for control of pathogenic organisms. Crop rotation though widely used, is not highly advantageous because of its limited utility in controlling the plethora of pathogens that afflict crops. Further, crop rotation results in diminished overall productivity owing to the low per acre return that is usually obtained from non-host crops. Use of pathogen-resistant varieties of crops has a vast potential. However, a severe lack of pathogen resistant varieties of many crops causes this mechanism to be limited in efficacy.
Soil fumigation is another tool used for the control of plant pathogens. Chief among the crops which benefit from soil fumigants are strawberries, grapes, peppers, onions, deciduous fruits and nuts, turf, cut flowers, and tree and seedling nurseries. Some of the most effective soil fumigants are methyl bromide, chloropicrin, 1-3 dichloropropene, dimethyl disulphide, propargyl bromide, and methylisothiocyanate, or their mixtures, which are selected in various ratios and strength, depending on the target soil pests and soil variances such as temperature, texture and moisture. Most soil fumigants are composed of organic chemicals that are distributed within the soil as gases to either inhibit or kill destructive organisms. Soil fumigants are chemical compounds in the form of sulphur containing compounds and halogenated compounds.
The soil fumigants owe their effectiveness as soil biocides to their gaseous nature that allows them to spread though soil easily and reasonably uniformly. For instance, a soil fumigant such as methyl bromide, a colorless gas at room temperature, is commonly compressed into liquid form for purposes of application. After application in liquid form, methyl bromide penetrates the soil rapidly through air spaces between soil particles and then kills or suppresses pathogenic organisms. Other soil fumigants such as chloropicrin are also commonly employed for the control of bacteria, fungi, and insects because they also display similar soil penetration capabilities.
Traditionally, a field is prepared prior to fumigation by tilling and irrigating the soil so as to ensure proper soil texture and moisture content of the soil. Typically following preparation is a process called pre-plant soil fumigation, in which a commercial fumigator enters the field with a tractor with a rear mounted tool bar, to which is attached plumbed shanks that penetrate the soil and deliver the pre-plant soil fumigant to the desired depth. If desired, the field then may be tarped with a polyethylene film, which is applied by a roller attached to the tractor. Normally, the field is ready for planting thereafter within two weeks.
However, soil fumigants suffer from several drawbacks. First, though effective in lighter, sandier soils, soil fumigants are not as effective in heavier soils. When used in lighter, sandier soils that have finer soil particles and more air spaces between them, the soil fumigant is able to thoroughly disperse and reach the target organism. With heavy or cloddy soils, fumigants injected into the soil cannot reach target organisms because air spaces between soil particles are blocked with water and tightly compacted. The large air spaces between clods in heavier soils serve as avenues for rapid dissipation of fumigants, thereby reducing periods of exposure of the soil fumigants to the soil and thus diminishing the efficaciousness on soil pathogens.
Another difficulty is that if the aforementioned soil fumigants are mixed in water, the mixture will often corrode the pipe or tubing carrying the fumigants to the soil, thus resulting in damage to the pipes.
Finally, traditional methods of soil fumigation may expose workers to soil fumigants. One of the concerns associated with the process of soil fumigation is worker exposure to soil biocides that may occur through contact or inhalation. For workers engaged in working with soil fumigants such as methyl bromide, chloropicrin, 1-3 dichloropropene, dimethyl disulphide, propargyl bromide, and methylisothiocyanate, and their mixtures, inhalation is the typical route of exposure.
One of the objects of the present invention is to address the aforementioned drawbacks associated with the prior art methods of soil fumigation.